The present invention relates to an imaging apparatus, in which a lens focuses light from a subject on a solid-state image pickup device to form an image and electrical charges in the solid-state image pickup device are outputted to electrically obtain the image of the subject, and to a light quantity regulating device for mechanically regulating a quantity of light in the imaging apparatus.
Generally, an imaging apparatus, widely known as a video camera and a digital camera, forms an image of a subject on a solid-state image pickup device such as a CCD for obtaining an image data converted photo-electrically in the image pickup device. Recently, a cell phone with a built-in camera has been widely used. Similar to a silver camera (film-based camera), such an imaging device has an image-forming lens equipped to an imaging lens-barrel for focusing light from a subject on a predetermined image-forming plane, and the solid-state image pickup device, such as a CCD, is provided on the image-forming plane. Also, a light quantity regulating device, such as an iris device and a shutter device, is incorporated in the imaging lens-barrel for regulating a quantity of light in the image pickup device.
There has been a need to make such an imaging apparatus, in particular the imaging lens-barrel, small for reducing a size of a camera apparatus or for incorporating the imaging apparatus into a cell phone or the like, thereby further reducing a size, weight and cost. Conventionally, the light quantity regulating device, such as a shutter device and iris device, is controlled such that a shutter blade remains closed while the camera apparatus is not in use, so that light does not reach the imaging plane. In the case of the silver camera, such a structure prevents film exposure while no shooting is executed, and in the case of the solid-state image pickup device, such a structure prevents intense light, such as sunlight, from entering the image pickup device.
That is, in the digital camera as well as the silver camera, the light quantity regulating device, such as a shutter, is controlled to stay in a so-called normal closed state for blocking light while the apparatus is not in use. Such a light quantity regulating device with a normal closed control has been disclosed in, for example, Japanese Patent (Kokai) No. 3205714. In the quantity regulating device, a shutter blade and an iris blade are separately incorporated in a base board and disposed in an imaging lens-barrel. An electromagnetic driving device is linked to the blade members. The shutter blade remains closed while the apparatus is not in use, that is, power of a driving device is turned OFF.
When the light quantity regulating device of the normal closed control type is applied to a digital camera with a solid-state image pickup device, as disclosed in Japanese Patent No. 3205714, the shutter blade in the closed state is driven to switch to an open state when the apparatus is turned on. When a user pushes a shutter button (release button) after monitoring an image for shooting, electric charges in the solid-state image pickup device are released (electrical reset) to start an exposure. After a predetermined exposure time, a current is supplied to the shutter driving device to move the shutter blade to a closed position. In the digital camera with the solid-state image pickup device, different from a silver camera, the shutter is held opened for a considerable time for the monitoring before the shooting. Accordingly, power is kept supplied to the driving portion of the light quantity regulating device, such as a shutter, thereby consuming extra power.
In order to solve the problem, in Japanese Patent No. 3205714, a driving device is formed of a magnet rotor and an exciting coil wound around the periphery of the rotor. Further, an attraction member made of a soft magnetic material is provided for holding the magnet rotor at an actuated position (closed position of the shutter) and a non-actuated position of the blade. Specifically, a pin made of a soft magnetic material is provided at just outside of a moving range of the magnet rotor, and a magnetic pole of the magnet rotor is attracted to the pin, so that the blade member is held at the open position or the closed position without a driving current.
In the conventional imaging apparatus with the solid-state image pickup device described above, when the shutter blade controls the exposure, the blade member stays at the closed position when the apparatus is not in use and moves to the open position when the apparatus is turned on. In this case, it is necessary to supply power to the driving device of the blade during the monitoring for relatively a long time, thereby wasting power. In order to eliminate this problem, in Japanese Patent No. 3205714, the light quantity regulating device is provided with a hold mechanism for holding the blade member at the open position after moving from the closed position. With the hold mechanism, it is not necessary to supply power to the driving device during the monitoring. However, it is necessary to provide the hold mechanisms at the open position and the closed position of the blade member separately. The hold mechanism includes a mechanical latch structure or a magnetic attraction structure disclosed in Japanese Patent No. 3205714.
When the pin members made of a soft magnetic material or the like are provided separately at the open position and the closed position of the blade for creating magnetic attraction, an exciting coil for inducing a driving force tends to have a small winding area, thereby increasing an outer shape of the apparatus for providing the winding area of the coil, and making it difficult to make the apparatus small. Further, when the charges in the solid-state image pickup device are successively transferred to outside after the blade member is closed, in the magnetic attraction mechanism for holding the blade at the closed position, the blade may rebound due to an impact at the attraction or sway toward the open position and vibrate due to an impact when an external force is applied to the camera apparatus, thereby leaking light from outside.
Further, when the special hold mechanism holds the shutter blade at the closed position magnetically or mechanically, there is an operational lag when the blade is released from the closed position in a case of successive shooting. For example, in the case of the magnetic attraction mechanism, a driving force of the exciting coil is reduced by an attraction force of the hold mechanism. Accordingly, the blade moves from the closed position to the open position slowly, thereby interfering the successive shooting.
In order to solve the problems described above, in the present invention, a shutter blade is held at an open position (posture) while not in use, different from the conventional normal closed control in which the shutter blade member is held at the closed position while not in use.
Accordingly, an object of the invention is to provide an imaging apparatus with a small lens-barrel with light weight and capable of shooting immediately after the apparatus is turned on or during the successive shooting.
Further objects and advantages of the invention will be apparent from the following description of the invention.